Amiloride inhibition of the Na+-H+ exchanger in renal microvillus membrane vesicles

Abstract

We examined the effect of amiloride on Na+-H+ exchange in rabbit renal cortical microvillus membrane vesicles. Amiloride inhibited both the uphill Na+ accumulation induced by imposition of a transmembrane Hin+ greater than Hout+ gradient and the uphill H+ efflux induced by imposition of a Naout+ greater than Nain+ gradient. The inhibitory effect of amiloride on Na+ influx was rapidly reversible and fully competitive (Ki 3.0 X 10(-5) M amiloride, KT 6.3 mM Na+). In addition, amiloride inhibited the efflux of Na+ from vesicles preloaded with Na+. However, the diuretic did not inhibit such other Na+-coupled transport processes as Na+-glucose ad Na+-alanine cotransport. These findings suggest that amiloride is a reversible, selective, competitive inhibitor for the Na+ site of the renal microvillus membrane Na+-H+ exchanger. Amiloride may, therefore, be useful as an experimental tool for investigating the role of Na+-H+ exchange in mediating proximal tubular acidification.

Volume-regulatory responses of Amphiuma red cells in anisotonic media. The effect of amiloride.

“…This mechanism appears to be similar to that in various cells including many "leaky" epithelia, such as gallbladder (Weinman and Reuss, 1982) and proximal renal tubule (Kinsella and Aronson, 1981 ;Boron and Boulpaep, 1983). It is noteworthy that the apparent amiloride-sensitive Na/H exchange mechanism of Necturus gallbladder (Weinman and Reuss, 1982) is postulated to be involved in the VRI response of these cells, with amiloride blocking volume recovery by osmotically shrunken cells Spring and Ericson, 1982).…”

“…Second, Na transport is enhanced beyond control levels after exposure of pretreated cells to control media when the cells have been pretreated with either amiloride-containing normal media or low-Na media (all solutions isotonic ; Ehrlich and Crabbe, 1968 ;Turnheim et al, 19'78) . Third, Na transport is a saturable function of external Na (Ussing, 1948;Frazier et al ., 1962 ;Kinsella and Aronson, 1981). Fourth, Li can substitute for Na, whereas K cannot (Zerahn, 1955 ;Lindley and Hoshiko, 1964 ;Herrera, 1972 ;Kinsella and Aronson, 1981).…”

“…In addition, amiloride appears to act as a competitive inhibitor of Na uptake in the Amphiuma red cell VRI response . Evidence that amiloride acts as a competitive inhibitor of Na transport has been presented in frog skin (Cuthbert and Shum, 1974 ;Fuchs et al ., 1977), toad bladder (Sudou and Hoshi, 1977), renal microvillus vesicles (Kinsella and Aronson, 1981), and trout gill (Greenwald and Kirshner, 1976). However, noncompetitive or mixed inhibition by amiloride has also been reported in epithelia (Benos et al, 1979) and cultured kidney cells (Rindler et al, 1979).…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…Consistent with this, global and proximal tubular NHE3 KO mice display a metabolic acidosis and alkaline urine [152,91]. Interestingly, NHE3 has been proposed to mediate NH 4 + efflux into the tubular lumen, although recent acid loading experiments on the proximal tubular KO mice are inconsistent with this [91,76]. Given the large amount of sodium and water which is not reabsorbed from the proximal tubule in the absence of NHE3 it is surprising the NHE3 KO mice survive at all.…”

The role of the transbranchial potential difference in hyperosmotic regulation of the shore crabCarcinus maenas

“…At higher concentrations (10-5-10 -3 M), the drugs affect the apical Na~/H+-exchanger (for further references see Benos et al, 1979;Kinsella & Aronson, 1981).…”